Journal ArticleDOI
The molecular structure and vibrational spectrum of the cyclopropenyl cation, C3H+3, and its deuterated isotopomers
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In this paper, the equilibrium structure, harmonic vibrational frequencies, infrared intensities, anharmonic constants, vibration rotation interaction constants and quartic and sextic centrifugal distortion constants of C3H+3, the cyclopropenyl cation, and its deuterated isotopomers have been determined via purely ab initio quantum-mechanical methods.Abstract:
The equilibrium structure, harmonic vibrational frequencies, infrared intensities, anharmonic constants, vibration–rotation interaction constants and quartic and sextic centrifugal distortion constants of C3H+3, the cyclopropenyl cation, and its deuterated isotopomers have been determined via purely ab initio quantum‐mechanical methods. Two one‐particle basis sets have been employed in conjunction with second‐order M≂ller–Plesset perturbation theory (MP2), singles and doubles configuration interaction (CISD), and singles and doubles coupled cluster (CCSD). The best estimate of the harmonic frequencies is obtained from MP2 with a triple zeta plus double polarization (TZ2P) basis set. The anharmonic analysis has been determined via second‐order perturbation theory using a double zeta plus polarization (DZP) self‐consistent‐field (SCF) full quartic force field. A generalization of formulas for the anharmonic analysis of D3h symmetric tops is discussed. The complete quartic force field in symmetry internal co...read more
Citations
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Journal ArticleDOI
An Accurate ab initio Quartic Force Field and Vibrational Frequencies for CH4 and Isotopomers
TL;DR: In this paper, a very accurate ab initio quartic force field for CH4 and its isotopomers is presented, for which the fundamental vibrational frequencies and the anharmonic constants are the most accurate estimates available.
Journal ArticleDOI
Highly accurate quartic force fields, vibrational frequencies, and spectroscopic constants for cyclic and linear C3H3(+).
TL;DR: It is expected that the fundamental vibrational frequencies and spectroscopic constants presented here are the most reliable available for the free gas-phase species, and it is hoped that these will be useful in the assignment of future high-resolution laboratory experiments or astronomical observations.
Journal ArticleDOI
The anharmonic force field and equilibrium molecular structure of ketene
TL;DR: In this paper, a comprehensive anharmonic vibrational analysis of isotopic ketenes has been performed on the basis of a complete ab initio quartic force field constructed by means of second-order Mo/ller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles (CCSD) approach, augmented for structural optimizations by a contribution for connected triple excitations [CCSD(T)].
Book ChapterDOI
Gaussian-based density functional methodology, software, and applications
TL;DR: Some of the progress made by the Universite de Montreal group over the last few years, and especially over recent months, towards developing, testing, and applying Gaussianbased density functional techniques of increased accuracy, speed and functionality are reviewed.
Journal ArticleDOI
The prediction of spectroscopic properties from quartic correlated force fields: HCCF, HFCO, SiH+3
TL;DR: In this article, the second-order Mo/ller-Plesset method was used to calculate the quadratic force constants for the full quartic fields. But the effects of using large basis sets were examined.
References
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Journal ArticleDOI
Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms
TL;DR: In this paper, the effects of contraction on the energies and one-electron properties of the water and nitrogen molecules were investigated, and the authors obtained principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations.
Journal ArticleDOI
Analytic evaluation of energy gradients for the single and double excitation coupled cluster (CCSD) wave function: Theory and application
TL;DR: The theory for the analytic evaluation of energy gradients for coupled cluster (CC) wave functions is presented in this paper, where explicit expressions for analytic energy gradient of the CC singles and doubles (CCSD) wave function for a closed-shell restricted Hartree-Fock reference determinant are presented and shown to scale as N6 where N is the one-electron number of atomic basis functions for the molecular system.